The present invention relates to a filter structure, in particular a particle filter for the exhaust gas from an internal combustion engine, the filter being of the type comprising:                at least first and second filter members provided with first and second faces located facing each other; and        a joint connecting said faces together and extending between said faces.        
Such structures are used in particular in devices for depolluting the exhaust gas from internal combustion engines. Such devices comprise an exhaust pipe including in series therein a catalytic purifier member and a particle filter. The catalytic purifier member is adapted to treat the polluting emissions that are in the gaseous phase, while the particle filter is adapted to retain the particles of soot emitted by the engine.
In known structures of the above-specified type (see EP-A-1 142 619, for example), the filter members comprise a set of adjacent ducts with parallel axes that are separated by porous filter walls. The ducts extend between an admission face for admitting the exhaust gas to be filtered and an exhaust face for exhausting the filtered exhaust gas. The ducts are also closed at one or other of their ends so as to define inlet chambers opening out to the admission face and outlet chambers opening out to the exhaust face.
Those structures are operated in a succession of filtering and regeneration stages. During filtering stages, the soot particles emitted by the engine become deposited on the walls of the inlet chambers. Head loss through the filter increases progressively. Beyond some predetermined value for said head loss, a regeneration stage is performed.
During the regeneration stage, the soot particles which are constituted essentially by carbon are burned on the walls of the inlet chambers so as to restore its original properties to the structure.
Nevertheless, soot particles do not accumulate in uniform manner within the filter members. Thus, soot accumulates preferentially in the center of the filter structure and towards the exhaust gas exhaust face. During regeneration stages, the burning of the soot raises the temperature in the preferential accumulation zones to a temperature higher than that observed in the other zones of the structure.
The temperature gradients within the filter structure lead to local expansions of different amplitudes, and consequently to longitudinal and transverse stresses in and/or to stresses between the various filter members.
These high levels of thermomechanical stress give rise to cracking in the filter members and/or in the connection joints between the filter members.
To limit the risk of such cracks appearing, patent application EP-A-1 142 619 proposes using connection joints of thickness selected to lie in the range 0.3 millimeters (mm) to 3 mm, and having thermal conductivity lying in the range 0.1 watts per meter kelvin (W/m.K) to 10 W/m.K.
Present structures do not give entire satisfaction. Beyond some number of regeneration stages, cracks can appear in the connection joints. These cracks are accompanied by a complete loss of cohesion in the filter structure. This loss of cohesion gives rise to leaks and the structure must be replaced.